The disclosure will deal with logs but some of the technology described will have another application. The term defects is intended to include one or more of stones or nails or other intrusions in the tree and natural defects such as knots or rot or very low density volumes or voids.
It has long been a desire of the forest products industry to provide a system for internally examining the log to find its defects and then, based on defects and their location, automatically in "real time" provide a sawing solution to permit maximization of the wood recovery or lumber recovery from the log. By "real time" it is meant at a rate that keeps pace with the normal speed of operation of the sawmill particularly the headrig of the mill.
In the Fourth Nondestructive Testing of Wood Symposium in August 1978 in a paper entitled "Scanning of and Computing Methods for Measuring Knots and Other Defects in Lumber and Veneer" by Torbjorm Schmidt there was a brief description of the application of tomography to investigate defects in a log. In that description the exposure time for tomography was 37 seconds and the computer took two minutes to provide the resulting picture illustrating a cross section through one section of the log. It will be apparent that, while it was evident one could determine the internal structure of a log using tomography in 1978, it was simply impossible to do this in a time frame that was useful for control in a sawmill. This is particularly true when one considers that only a single cross sectional image was obtained in a two and half minute time frame.
In Wood Science (Vol 14, No. 3, p 97-104, January 1982) an article entitled "Application of Automatic Image Analysis to Wood Science" by Charles W. McMillan discusses automatic image analysis and describes scanning technology for primary log breakdown and for cutting clear furniture parts from defective boards. The use of computerized axial tomography "CATSCAN" to nondestructively locate defects in the log interiors is described.
The majority of the McMillan paper is directed toward image analysis of photographic images and is simply an indication of what might be accomplished. However none of the operations are done in "real time". These teachings are not useful for a commercial log scanner to determine a sawing solution in "real time".
In the McMillan article the concept of using a CATSCAN to determine the interior of a log is discussed as well the use of a plurality of such scans to define the x-y coordinates for a knot in each such cross sectional scan. McMillan suggests that the information from the cross sectional scans then be used in a computer to determine the log positions needed to maximize grade or value yield but provides no teaching on how this might be done.
In Forest Research Bulletin No. 8 (Feb. 19, 1982) there is a paper entitled "Computed Tomographic Scanning for the Detection of Defects within Logs" by Benson-Cooper et al. that also suggests that a sawing solution based upon CATSCAN information might be derived, but does not provide any teaching as to how one might obtain this objective.